Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

342 Biological Control of Insect Pests: Southeast Asian Prospects
Young female wasps are better than old at searching for eggs. At 14.8¡C
and 28.9¡C the period from egg to first adult emergence was 122.9 and 22.4
days respectively and the duration of a generation was 162.7 and 31.2 days.
The life span of a female wasp fed on a diet of 20% levulose solution was
30.3 days at 14.8¡C and 28 days at 35.6¡C. Synchronisation of the parasite to
T. ni was found to be nearly perfect at 25¡C. At some temperatures the
parasitoid killed host eggs and at others, larvae before the 5th instar: this
resulted in the death of the contained parasitoids (Stoner and Weeks 1974,
1976).
T. ni larvae parasitised by C. truncatellum consumed 35% more food and
had a 30% higher maximum weight than unparasitised larvae, which raises a
concern for at least the short-term effect of biological control (Hunter and
Stoner 1975). The mortality caused by C. truncatellum appeared to be
density related (Ehler and van den Bosch 1974). Average parasitisation of
T. ni eggs in the laboratory was 55.3% (McPherson 1993). However, the
maximum recorded in cotton fields in southern California was 2.5% (Ehler
1977a).
C. truncatellum has been reported from larvae of Noctuidae,
Geometridae, Cossidae and Coleophoridae (Peck 1963). However, Ehler
(1977a) points out that it has been reported only from T. ni in Californian
cotton (van den Bosch and Hagen 1966; Ehler and van den Bosch 1974) and
that it appears to be specific in this environment. C. truncatellum has a
Holarctic distribution, but its native home is not clear (Peck 1963).
Cotesia marginiventris Hym.: Braconidae
More eggs were laid by this generalist larval parasitoid in 2-day-old T. ni
larvae than in younger or older larvae. The minimum development period
from oviposition to adult emergence from the host was 6 days (Boling and
Pitre 1970). Females were significantly more responsive to host odors after
brief contact with host larval frass or host-damaged cotton leaves (Turlings
et al. 1989). C. marginiventris from T. ni and 4 other species of noctuid
larvae were found to contain a non-occluded, filamentous, baculo-like virus
(Styer et al. 1987).
Hyposoter exiguae Hym.: Ichneumonidae
This solitary endoparasitoid is one of 3 main parasitoids of T. ni on cotton
(Ehler 1977a) and other crops in California and has a modest ability to
distinguish unparasitised from parasitised hosts (Beegle and Oatman 1975;
Browning and Oatman 1984). The female prefers to oviposit in late 1st or
2nd instar T. ni larvae, although all instars are acceptable. When early instars
are chosen, the host larvae generally die during the 3rd or 4th instar (Ehler
1977a). Parasites commencing their development in hosts 1-day-old took